I've found this design to be handy for backpacking and a sturdy alternative to
commerically made hammocks. When stringing your hammock using a vinyl tarp, DO NOT attempt to use the existing grommets. They will tear out quickly, leaving you in pain flat on your back.

1) Begin with an 8X10 tarp and fold it once lengthwise.

2) Where the center three grommets line up, tie the edge of the tarp together with nylon or poly rope.

I mean do an accordian fold
about 3 inches deep across the edge. Essentially you want to gather the
edge evenly before you tie it.
3) At each end of the tarp make an accordian fold about 3 inches deep across the edge and tie off with a clove hitch about 6 inches in from the edge of the tarp using a quarter-inch nylon rope. You need to gather the edge evenly before you tie it. Use about 25 feet of rope at each end of your hammock.

4) From the clove hitch to the edge of the hammock, tie a series of half hitches. The edge of the tarp with its cord in the hem and the other grommets will form a natural bulge. At this point finish off with another clove hitch.

5) To hang your hammock find two trees or other solid anchors about 12 to 14 feet apart. (don't exceed this by much or you will have to hang your hammock too high to compensate for the sag factor.)

6) Hang the hammock about waist high and stretch it as tight as you can. If you have enough rope at each end it doesn't hurt to wrapp it twice around the tree, back to the end of the hammock, out again to the treet, wrap and then finish with a clove hitch at the hammock. this provides extra cords supporting your weight.

8) Enter the hammock by sitting down at the center, lay down and at the same time swing your legs up. If you are centered on the hammock, its edges should rise 6 inches or so and give you plenty of safe support.

This also makes a comfortable camp chair. You can sleep looking up at the stars, or if weather threatens, use a second tarp overhead as an awning by tying a line about 3 feet above you between your support trees. It's also easy to insert netting under the fly or use instead of the fly when you are camping in bug country.